Ultrafast time hopping CDMA-RF communications: code-as-carrier, multichannel operation, high data rate operation and data rate on demand

ABSTRACT

An ultrashort pulse time hopping code-division-multiple-access (CDMA) RF communications system in the time-frequency domain comprises a transmitter including a short duration pulse generator for generating a short duration pulse in the picosecond to nanosecond range and a controller for controlling the generator, code means connected to the controller for varying the time position of each short pulse in frames of pulses in orthogonal superframes of ultrafast time hopping code division multiple access format, precise oscillator-clock for controlling such timing, encoding modems for transforming intelligence into pulse position modulation form, antenna/amplifier system. A homodyne receiver is provided for receiving and decoding the coded broadcast signal, and one or more utilization devices are connected to the homodyne receiver. Preferably, the codes are orthogonal codes with the temporal coding of the sequence of ultrafast, ultrawideband pulses constituting the carrier for transmission by the antenna system. The homodyne receiver includes a bank of decoder/modems, an acquisition system/matched filter for synchronizing to a superframe transmission, identifying coded sequencers in the superframe and assigning the transmissions to a selected decoder/modem on the basis of code recognition. The system is adapted for multichannel operation and provides a high overall data rate in the 500 mbs range for maximum multichannel operation.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION

The present invention relates generally to wireless RF time hoppingcode-division-multiple-access (CDMA) spread spectrum communicationssystems, and specifically to ultrafast systems, which use individualultrashort pulses (monocycle) signals in the picosecond (10⁻¹²) tonanosecond (10⁻⁹) range. Such ultrashort pulsed (monocycle) signals canalso be very wide in instantaneous bandwidth. Before transmission andafter reception, the system functions as a digital communicationssystem. The carrier for such wireless communications systems is neithera frequency, amplitude, phase nor polarization carrier, but is due tothe precise timing arrangements in a sequence of individual pulsesprovided by the digital coding schemes.

Whereas most wireless RF communications systems in the art usefrequency-domain receiver designs based on the heterodyne, or superheterodyne principle, the receiver of the present invention is atime-domain homodyne receiver. Whereas prior art uses coding, e.g., indirect sequencing or frequency hopping, to achieve spreading anddespreading of the signal with resultant processor gain, the presentinvention uses an ultrashort pulse as an individual signal always spreadover a very wide bandwidth, as well as coding which determines thetiming of such individual pulses within a sequence. Information iscarried in a transmission by the pulse position modulation technique,i.e., by precise micro-deviation from the pulse sequence timing set bythe channel code.

Due to the use of orthogonal coding schemes and the use of ultrafastpulse sequence techniques, it is possible to provide extremely high datarate wireless point-to-point communications, as well as wide-area voiceand data communications.

Accordingly, it is an object of the present invention to significantlyincrease the data rate of wireless RF communications by using orthogonalcoding schemes in ultrafast time hopping CDMA communications both inpoint-to-point and broadcast mode.

It is a further object of the invention to provide a communicationssystem which can coexist without interfering with, or causinginterference to conventional RF transmissions or other ultrafast timehopping CDMA users.

It is a further object of the invention to provide a wirelesscommunications system which can interface with digital, e.g., opticalfiber, communications systems.

It is a further object of the invention to provide a communicationssystem which is robust against environmental notched filtering offrequency components in the transmitted signal.

It is a further object of the invention to provide a communicationssystem which has substantial range at modest power, is small in size,weight and is not costly to manufacture.

SUMMARY OF THE INVENTION

Briefly, the above and other objects of the present invention areachieved in an RF ultrafast time hopping CDMA wireless communicationssystem, which uses individual pulses in a sequence of such pulses, thoseindividual pulses being so short in duration (e.g., in the picosecondand nanosecond range) that the individual pulse signal energy is spreadover very many frequencies simultaneously or instantaneously (instead ofsequentially). A time hopping sequential code is also used to positionthese pulses precisely in sequence providing optimum use oftime-frequency space and also providing noninterfering transmissionchannels due to the orthogonality of the coding schemes used.

The ultrashort nature of the individual pulses used also permits thetime duration of a frame to be divided into very many microintervals oftime in which the signal could occur. This division into very manymicrointervals in a frame permits the availability of many possiblecoding schemes as well as many noninterfering transmission channels.Thus the ultrashort nature of the individual pulses, together withorthogonal coding schemes, permits the highest multichannel data ratesof any wireless communications system.

In one embodiment of the present invention a communications system uses:(i) orthogonal codes which can be slaved to a single acquisitionsystem/matched filter and which captures and assigns each code to unquedecoding modems; (ii) correlators/acquisition systems/matched filterswhich are able to detect the ultrafast, ultrawideband signals and retainmemory of such capture over superframes of the order of a millisecond;(iii) pulsed power sources, antennas, encoding modems,oscillator-clocks, intelligence/data encrypters; and (iv) EPROMs toprovide coding information to both encoding and decoding modems.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the inventionwill become more apparent when considered with the followingspecification and accompanying drawings wherein:

FIG. 1a is a block diagram of a transmitter incorporating the inventionconfiguration for an ultrafast time hopping CDMA wireless communicationssystem, and FIG. 1b is a block diagram of a receiver configurationthereof,

FIG. 2 illustrates frames and subframes in an ultrafast time hoppingCDMA wireless communication system incorporated in the invention.

FIG. 3 is a diagrammatic exposition of the subframe, frame andsuperframe,

FIG. 4 is a diagrammatic exposition of one method for achievingcorrelation and subframe sampling,

FIGS. 5a, 5b and 5c illustrate two orthogonal codes (FIG. 5a and 5b),and their auto- and cross-correlation (FIG. 5c),

FIG. 6 illustrates a hyperbolic congruence code, p=11, a=1, 10×10matrix,

FIG. 7 illustrates a hyperbolic congruence code, p=11, a=1, 50×50matrix,

FIG. 8 illustrates the autoambiguity function for the hyperboliccongruence codes, p=11, a=1 and p=11, a=3, 10×10 matrix,

FIG. 9 illustrates the crossambiguity function for the hyperboliccongruence codes, p=11, a=1 and p=11, a=3, 10×10 matrix,

FIG. 10a illustrates a time-frequency representation of an ultrashortpulse of 1 nanosec. and a synchronous (e.g., heterodyne) receiver for anarrow-band sinusoid, and FIG. 10b is a bird's-eye-view of FIG. 10a.

FIG. 11 is a cut through the three-dimensional of FIG. 10,

FIG. 12 illustrates an acquisition system according to the invention,and

FIG. 13 illustrates a detail of the acquisition system and decodemodems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In general physical terms the present invention is a system illustratedin FIGS. 1a and 1b. The various component parts are described in theSystem section and the specifics of the coding schemes are described inthe Codes section.

THE SYSTEM

There are many possible embodiments of an ultrafast time hopping CDMAsystem. The following is an embodiment which permits multichannel (highdata rate) use.

1. Oscillator Clock 10, 10'. This circuit can use, e.g., GaAs MMICtechnology, or other semiconductor technology, to convert DC power to a2 GHz signal. The output signal of the oscillator clock will havesufficient power to drive the data gate circuitry and transmitteramplifier (during transmission of a pulse). The oscillator clock is acrucial subcomponent requiring an accuracy >20 picoseconds in 1 msec.,or about 20 parts in 10⁹.

The signal can be generated by a voltage-controlled oscillatorphase-locked to a frequency stable reference signal.

2. Pulse Emitter and Antenna Module TA. During the transmission of anon-going pulse a sample of the oscillator signal is amplified andtransmitted out of the antenna. An RF switching circuit (in pulsegenerator PG) driven by the comparator COMP trigger permits theoscillator clock to drive the transmitter amplifier chain for theduration of the pulse. The transmitter amplifier chain delivers theresulting RF pulse to the antenna at a power level required by thesystem.

The amplifier can be, e.g., a cascaded set of GaAs MMIC chips, or othersemiconductor technology. The bandwidth and impedance matching of theseamplifiers can be achieved by, e.g., a distributed network of parallelMESFETs, or by other semiconductor methods. The input and outputparasitic capacitances of the devices is absorbed by series inductanceswhich in effect form a lumped element 50 ohm transmission line.

The antennas per se for both transmit and receive used can either be ofthe nonresonant kind or nondispersive TEM horn designs. In either case,printed circuit methods can be used to fabricate the antennas on thecircuit boards, as well as other methods of fabrication.

3. Acquisition Module AM. The acquisition module can be based on designsusing associative string processor technology or other means. Thismodule is described in detail below.

4. Modems/Encoders and Modems/Decoders (Data Gate Circuitry). The datagate circuitry is common to both the transmitter and receiver. It canconsist of, e.g., very high precision GaAs digital circuitry, or othersemiconductor circuitry. The subframe counter is a free running counterdriven by the clock oscillator. The output of the counter is compared tothe look-up code corresponding to the frame counter.

The digital gate circuitry can be achieved using, e.g., ECL compatiblesource coupled logic on GaAs, or other semiconductor technology. Gatelength and width can be chosen to reduce the parasitic capacitances suchthat loaded gate speed of less than 50 picoseconds can be met.

The receiver data gate counters are reset when a transmission isreceived. A high speed data latch is triggered to capture the output ofthe pulse detector during the subframes triggered by the code. Theoutput of the data latch contains the transmitted data including errorcorrection which corresponds to the position of the pulse within thesubframe.

The transmitter data gate subframe and frame counters are free running.Whenever the subframe counter and codes match the pulse generator istriggered causing a high speed pulse to be transmitted. The pulseposition in the subframe corresponds to the data and error correctioncodes of the least significant bits at the inputs to the AcquisitionModule.

5. Code EPROMs (Code Look-up 14, 14'). The code generation function canbe performed by EPROMs in code look-up 14, 14' in the transmitter andreceiver. Once per frame, a pulse is generated by the frame counterEPROM. The code specifies in which subframe the pulse will occur. Withthe use of more than one code (data rate on demand) the EPROM willprovide more than one code to the transmitter and receiver.Alternatively, phase-shift registers can be used to generate the codes.

6. Pulse Detector (Rise Time Trigger 15). Background interference can berejected by a rise-time triggering circuit, which is not merely a highpass filter. (An ultrashort pulse with a 4 GHz bandwidth containsextremely low frequency components. Therefore a high pass filterdistorts the ultrashort pulse). In order to achieve rise-timetriggering, the RF signal can be passed through an envelope detectorwhich is then fed through a high-pass filter before reaching the triggerthreshold circuit. The high pass filter then differentiates the envelopeand passes transients while rejecting slow changes.

7. Receiver (FIG. 1b). The receiver is a homodyne receiver (not aheterodyne receiver). The receiver preamplifier (not shown) needs amaximum of 40 db gain, no AGC, and a noise figure of approximately 5 db.The bandwidth required is about 4 GHz. The preamplifier of the receiverantenna RA feeds a pulse detector 15 which output and ECL pulse for eachdetected pulse. The pulse detector 15 feeds the Acquisition Module AM,which includes correlator CO' which output triggers to the frame counterFC' and subframe counter SC'. The remainder of the receiver is similaror complementary to the transmitter. In a preferred embodiment, ahigh-speed counter SC' gates a data latch DL when the counter valuematches the current main code value. The high-speed counter SC' wrapsaround at each frame interval. This wrap increments a frame counter FC',which is used to look up the code commencement in the EPROM 14'. Theframe counter FC' wraps around at each superframe interval. The datalatch DL' feeds the FEC decoder FEC' and optional decryptor DEC, whichoperates at the frame rate (about 1 Megabit per second). The receiverdesign is further described below.

With the use of multiple codes (data rate on demand) the EPROM 14', orphase-shift register, or other means of code generation, will providemore than one code to both the receiver and transmitter.

THE CODES

The wireless communications network can be used in either network orduplex arrangements. Two levels of coding are used in systems of thepresent invention. the major code is used to time the pulse transmissionand allow multiple channels. Additionally, a forward error correction(FEC) code is applied to the informational data before transmission.There is a large choice of error correcting codes (see Cipra, 1994).

The use of orthogonal codes permits the coexistence of multiple channelsslaved together in the same superframe of a matched filter.Representative such codes are Quadratic Congruence (QC) codes,Hyperbolic Codes (HC) codes and optical codes (Titlebaum & Sibul, 1981;Titlebaum et al, 1991; Kostic et al, 1991). The discussion of codingrequirements will be based on these codes.

The method for generating the placement operators for the QC code familyprovides a sequence of functions defined over the finite field, J_(p),where:

    J.sub.p ={0,1,2, . . . ,p-1},

and p is any odd prime number. The functions are defined as:

    y(k;a,b,c)=[ak.sup.2 +bk+c].sub.modp,kεJ.sub.p,

where a is any element of J_(p) except O and b,c are any member ofJ_(p). The parameter a is called the family index.

The difference function for the HC codes is the ratio of two quadraticcongruences. The denominator polynomial of the ratio cannot have anyzeros and the numerator is quadratic and has at most two zeros.Therefore, the HC codes have at most two hits for any subframe or frameshift. A sequence, u_(m) (i),i=0,1,2, . . . ,n-1, which is a member of atime hopping code can be constructed according to a method shown in FIG.2. For example, pulses received in the first interval of themacro-window signify "1" and those received in the second intervalsignify "0". The number of bits in the subframe (microwindow) isdetermined by the precision of the data gate circuitry. Alternatively,the subframe can be used to encode analog information.

FIG. 5 shows the auto- and cross-correlation of two orthogonal codes.The autocorrelation is excellent indicating excellenttransmission/reception capabilities. The crosscorrelation is extremelyflat, indicating excellent crosschannel interference rejection.

FIG. 6 and FIG. 7 shows two HC codes, p=11, a=1, 10×10 matrix, FIG. 6,and, p=11, a=1, 50×50 matrix, FIG. 7 and FIG. 8 shows the autoambiguityfunction, for the HCC code, p=11, a=1, 10×10 matrix and FIG. 9 shows thecross-ambiguity function, for the HC codes, -=11, a=1 and p=11, a=3,10×10 matrix.

The QC codes are defined as: ##EQU1## with 1≦a≦p-1 and 0≦x≦p-1 for p×pmatrices.

The HC codes are defined as:

    y.sub.a (x)=i/xmodp,

where 1/x is the multiplicative inverse in the field J_(p) and with1≦a≦p and 1≦x≦p for p-1×p-1matrices.

The QC and HC codes, due to Titlebaum and associates (Albicki et al,1992; Bellegarda & Titlebaum, 1988-1991; Drumheller & Titlebaum, 1991;Kostic et al, 1991; Maric & Titlebaum, 1992; Titlebaum, 1981; Titlebaum7 Sibul, 1981; Titlebaum et al, 1991), are orthogonal codes for use inthe present invention, the ultrafast time hopping CDMA communicationsystems. Other choices are available in the literature.

The major codes used in systems of the present invention are equallyapplicable to optical orthogonal coding procedures for fiber opticalcommunications. The use of orthogonal codes permits the coexistence ofmultiple channels slaved together in the same superframe of a matchedfilter. For ease of explanation, the following terms are defined inTable 1.

                                      TABLE 1                                     __________________________________________________________________________    Subframe                                                                            The, e.g., ˜1 nanosecond interval during which a pulse is               transmitted.                                                                  The pulse is modulated by adjusting its position within the                   interval to                                                                   one of two or more possible times. For example, to send one bit               per                                                                           subframe, the pulse may be offset from the center of the subframe             by                                                                            ˜250 picoseconds for a zero, or +250 picoseconds for a one.       Frame A, e.g., ˜1 microsecond, interval, divided into approximately           1000                                                                          subframes (or according to the code length). A pulse is                       transmitted                                                                   during one subframe out of each frame. The pulse is sent during a             different subframe for each frame and according to the code.            Superframe                                                                          A, e.g, ˜1 millisecond, interval, representing one repetition           of a code                                                                     pattern. In the present example, approximately 1000 pulses are                transmitted during one superframe, at pseudorandom spacing.             Channel                                                                             One unidirectional data path using a single orthogonal code. The              raw                                                                           (uncorrected) capacity of one channel using a code of length 1020             is                                                                            approximately 0.5 mbs. Using all 1020 codes, the channel data rate            is                                                                            approximately 500 mbs.                                                  __________________________________________________________________________

An example of the relations between subframe, frame, superframe andchannel is given in Table 2 for a code of length 1020, Table 3 for acode of length 508, and Table 4 for a code of length 250.

                  TABLE 2                                                         ______________________________________                                        largest count of code       1021                                              modulation                                                                    code period  1021 - 1       1020 frames                                       hop slot duration           695 picoseconds                                   (the subframe)                                                                frame time interval                                                                        927 × 10.sup.-12 × 1020                                                          950 nanoseconds                                   (the frame)                                                                   time of one complete                                                                       1020 × 950 × 10.sup.-9                                                           0.97 milliseconds                                 code period                                                                   (the superframe)                                                              fraction of frame time for encoding                                                         ##STR1##      0.75                                              forward error cor-          2                                                 recting redundancy                                                            data interval                                                                              2 × 950 × 10.sup.-9                                                              1.9 microseconds                                  data encoding interval                                                                     2 × 695 picoseconds                                                                    1.39 nanoseconds                                  subframe                                                                      data rate                                                                                   ##STR2##      ˜526 kbs                                    data frame subinterval      347.5 picoseconds                                 data frame bandwidth                                                                        ##STR3##      1 bit                                             single channel data                                                                        1 × 526 × 10.sup.3                                                               ˜526 kbs                                    rate                                                                          maximum number of           1020                                              codes                                                                         multichannel data rate                                                                     10 × 526 × 10.sup.3                                                              5.26 mbs                                          using 10 codes                                                                multichannel data rate                                                                     1020 × 526 × 10.sup.3                                                            537 mbs                                           using the maximum                                                             number of codes                                                               ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        largest count of code       509                                               modulation                                                                    code period  509 - 1        508 frames                                        hop slot duration           695 picoseconds                                   (the subframe)                                                                frame time interval                                                                        927 × 10.sup.-12 × 508                                                           472 nanoseconds                                   (the frame)                                                                   time of one complete                                                                       508 × 472 × 10.sup.-9                                                            0.24 milliseconds                                 code period                                                                   (the superframe)                                                              fraction of frame time for encoding                                                         ##STR4##      0.75                                              forward error cor-          2                                                 recting redundancy                                                            data interval                                                                              2 × 472 × 10.sup.-9                                                              0.94 microseconds                                 data encoding interval                                                                     2 × 695 picoseconds                                                                    1.39 nanoseconds                                  subframe                                                                      data rate                                                                                   ##STR5##      ˜1059 kbs                                   data frame subinterval      347.5 picoseconds                                 data frame bandwidth                                                                        ##STR6##      1 bit                                             single channel data                                                                        1 × 1059 × 10.sup.3                                                              ˜1059 kbs                                   rate                                                                          maximum number of           509                                               codes                                                                         multichannel data rate                                                                     10 × 1059 × 10.sup.3                                                             10.59 mbs                                         using 10 codes                                                                multichannel data rate                                                                     509 × 1059 × 10.sup.3                                                            539 mbs                                           using the maximum                                                             number of codes                                                               ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        largest count of code       251                                               modulation                                                                    code period  251 - 1        250 frames                                        hop slot duration           695 picoseconds                                   (the subframe)                                                                frame time interval                                                                        927 × 10.sup.-12 × 250                                                           233 nanoseconds                                   (the frame)                                                                   time of one complete                                                                       250 × 233 × 10.sup.-9                                                            0.06 milliseconds                                 code period                                                                   (the superframe)                                                              fraction of frame time for encoding                                                         ##STR7##      0.75                                              for encoding                                                                  forward error cor-          2                                                 recting redundancy                                                            data interval                                                                              2 × 233 × 10.sup.-9                                                              0.47 microseconds                                 data encoding interval                                                                     2 × 695 picoseconds                                                                    1.39 nanoseconds                                  subframe                                                                      data rate                                                                                   ##STR8##      ˜2130 kbs                                   data frame subinterval      347.5 picoseconds                                 data frame bandwidth                                                                        ##STR9##      1 bit                                             single channel data                                                                        1 × 2130 × 10.sup.3                                                              ˜2130 kbs                                   rate                                                                          maximum number of           251                                               codes                                                                         multichannel data rate                                                                     10 × 2130 × 10.sup.3                                                             21.3 mbs                                          using 10 codes                                                                multichannel data rate                                                                     250 × 2130 × 10.sup.3                                                            533 mbs                                           using the maximum                                                             number of codes                                                               ______________________________________                                    

The subframe, frame and superframe relations are shown in FIG. 3.

THE RECEIVER

In conventional frequency domain heterodyne receivers the mixer is byfar the preferred front-end component. In general, mixers are used toconvert a low-power signal from one frequency to another by combining itwith a higher-power local oscillator (LO) signal in a nonlinear device.Usually, the difference frequency between the RF and LO signals is thedesired output frequency at the intermediate frequency (IF) atsubsequent IF amplification. Mixing with local oscillators downconvertsto intermediate frequencies and in the IF section narrowband filteringis most easily and conveniently accomplished. Subsequent amplificationand detection is based on the intermediate frequency signal.

The operation of a detector in the mixing code results in a much lowerconversion loss and is the reason for the excellent sensitivity of thesuperheterodyne receiver. The mixing action is due to a nonlineartransfer function:

    I=f(V)=a.sub.0 +a.sub.1 V+a.sub.2 V.sup.2 +a.sub.3 V.sup.3, . . . a.sub.n V.sup.n,

where I and V are the receiver current and voltage If V_(RF) sinω_(RF) tis the RF signal and V_(LO) sinω_(LO) t is the LO signal, then themixing products are:

    I=a.sub.0 +a.sub.1 (V.sub.RF sin ω.sub.RF t+V.sub.LO sin ω.sub.LO t)+a.sub.2 (V.sub.RF sin ω.sub.RF t+V.sub.LO sin ω.sub.LO t).sup.2 ++a.sub.3 (V.sub.RF sin ω.sub.RF t+V.sub.LO sin ω.sub.LO t).sup.3, . . . a.sub.n (V.sub.RF sin ω.sub.RF t+V.sub.LO sin ω.sub.LO t).sup.n.

The primary mixing products come from the second-order term. However,many other mixing products--may be present within the IF passband.Mixing produces not only a new signal but also its image, i.e., ω_(LO)±ω_(RF). However, in the case of ultrafast time domain signals, whichare ultrawideband, filtering would severely limit the amplitude of thesignal and hence its range.

For example, the second-order term for a narrow-band frequency domainsignal is:

    a.sub.2 (V.sub.RF sin ω.sub.RF t+V.sub.LO sin ω.sub.LO t).sup.2

but for a broad-band time domain ultrafast signal it is:

    a.sub.2 (V.sub.RF.sbsb.1 sin ω.sub.RF.sbsb.1 t+V.sub.RF.sbsb.2 sin ω.sub.RF.sbsb.2 t+V.sub.RF.sbsb.3 sin ω.sub.RF.sbsb.3 t+V.sub.RF.sbsb.i sin ω.sub.RF.sbsb.i t+ . . . V.sub.LO sin ω.sub.LO t).sup.2

The output is then: ##EQU2## which possesses too many intermodulationproducts for use as an IF input.

Therefore, due to the broadband nature of the ultrafast, ultrawidebandindividual signal, the synchronous (super) heterodyne receiver shouldnot be the choice in receivers of the present invention due to thenumber of mixing products produced. The receiver of choice for thepresent invention is a homodyne receiver.

A problem in definition arises in the case of the homodyne receiver. Wetake our definitions from optical physics (Born & Wolf, 1970; Cummins &Pike, 1974), not from radar engineering. Essentially, the heterodynemethod requires a local oscillator to be mixed with the received signaland is a "self-beat" or autocorrelation method. The homodyne method isinherently a coherent method [cf. Born & Wolf, 1970, page 256]. Theheterodyne method can be used with autocorrelation methods, e.g., afterthe mixing operation. The heterodyne method can even use a "coherent"local oscillator, but only with a narrowband signal. The distinguishingfeatures between the two methods are that the homodyne method is acoherent (correlative) signal acquisition method with (a) norestrictions on the bandwidth of the received signal and (b)restrictions on the absolute timing of the signal bandwidth components.Conversely, the heterodyne method is a signal acquisition method with(a) no restrictions on the timing of the received signal and (b)restrictions on the bandwidth of the signal frequency components.

The various definitions of the heterodyne and homodyne methods are notconsistent. For example, the IEEE Standard Dictionary of ElectronicTerms (Jay, 1988) defines "homodyne reception" as "zero-beat receptionor a system of reception by the aid of a locally generated voltage ofcarrier frequency"; and the McGraw-Hill Dictionary of Science andTechnology (Parker, 1989) defines "homodyne reception" as "a system ofradio reception of suppressed-carrier systems of radio telephony, inwhich the receiver generates a voltage having the original carrierfrequency and combines it with the incoming signal. Also known aszero-beat reception."

Essentially, these definitions (Jay, 1988; Parker, 1989) refer to thegeneralized use of homodyning in a receiver with more than one mixingstage. "Synchronous" detection is achieved by a method called"homodyning", which involves mixing with a signal of the same frequencyas that being detected either by external or internal (i.e., with aphase loop) methods. Thus, recently the term "homodyne" has come to meana method for the detection of narrowband signals and for restoring asuppressed carrier signal to a modulated signal.

Clearly the waters have been muddied concerning the definitions of theheterodyne and homodyne methods. However, the original optical physicsdefinitions are specific in equating heterodyning as a method of signalacquisition using a local oscillator, and homodyning as a method ofsignal acquisition using a coherent method such as autocorrelation.Ultrafast, ultrashort pulse signal acquisition requires the homodynemethod because it is a coherent method and preserves timing information.It would not be right to coin new terms, because the present termscontinue to survive relatively unambiguously in optical physics fromwhence they came. Therefore, we shall use the terms in the opticalphysics sense of those terms, but cautiously recognizing the danger oftriggering the wrong associations.

The distinction between homodyne and heterodyne reception is significantand bears on the claims that the present invention is noninterfering toconventional, i.e., heterodyne, receivers. In FIGS. 10a and 10b, isshown both ultrafast, ultrashort pulse homodyne reception andnarrow-band synchronous signal heterodyne reception in time-frequencyspace. FIG. 10a is a time-frequency representation of an ultrashortpulse of 1 nanosec. and a synchronous (e.g., heterodyne) receiver for anarrow-band sinusoid. Looking only from the frequency axis, the(exaggerated) spike of the ultrashort pulse would appear to overlap withthe rising ridge of the narrow-band heterodyne receiver, i.e., theheterodyne receiver would appear to receive any of the ultrafast,ultrashort signals. However, looking at the total time-frequency planerepresentation, it can be seen that the ridge representation of thenarrow-band synchronous heterodyne receiver does not extend down to therepresentation of the ultrafast signal representation. The synchronous,heterodyne receiver takes some time to respond and requires a number ofcycles of a signal to receive that signal.

The distinction between the homodyne reception of the present inventionand conventional heterodyne reception is shown in FIG. 11, which is acut through FIG. 10a and viewed from the time side. The ultrafast,ultrashort pulse signal is shown to be diminished in amplitude forconventional heterodyne receivers of all attack (rise) times, even ifthe ultrashort signal's average frequency is at the center frequency ofthe heterodyne receivers. On the other hand, homodyne receptionpreserves signal amplitude and timing.

THE ACQUISITION SYSTEM

The acquisition system/matched filter of the present inventionrecognizes multiple codes (channels) over a superframe time period (1msec. for a 1020 length code). FIG. 12 shows an Acquisition System, H,receiving F wireless signals from four channels S₁ -S₄ in asynchronouswraparound and triggers the receiving system decoding modems, S₁ -S₄.

FIG. 13 shows an embodiment in which the superframe of eachtransmission, S₁ -S_(n), e.g., with codes of length 1020, is preceded bya preamble frame, e.g., of length 10. This preamble must be received indouble wraparound for the case in which the channels, S₁ -S_(n), areunsynchronized in their transmissions. In this embodiment, the preambleis the same code for all channels, even if unsynchronized, and acts as asynchronization alert to the Acquisition System, which performsrecognition of the channel code and assigns a decoding modem. Unlike inthe embodiment of FIG. 12, in the embodiment of FIG. 13 the AcquisitionSystem is not functioning in wraparound mode, but is alerted to thebeginning of a transmission of a superframe by the preamble, which is indouble wraparound.

THE NETWORKS

The network applications of the present invention are diverse and rangefrom high data rate duplex systems, to building-to-building systems, tothe linking of optical fiber networks between such buildings, to withinbuilding communications, to LANs and WANs, to cellular telephones, tothe "last mile" of Global Grid communications, and to "smart highway"applications (Varaiya, 1993) (e.g., intelligent windshields, etc), etc.

APPLICATION AREAS OF THE PRESENT INVENTION

Wireless WANs and LANs;

Personal Communications Networks;

Cellular Telephones;

Building Automation/Security Systems;

Voice communications;

Bridge & Router Networking;

Instrument Monitoring;

Factory Automation;

Remote Sensing of Bar Codes;

Vehicle Location;

Pollution Monitoring;

Extended-Range Cordless Phones;

Video TeleConferencing;

Traffic Signal Controls;

Medical Monitoring and Record Retrieval Applications;

Remote Sensing;

Factory Data Collection;

Vending Machine Monitoring;

"Last Mile" Global Grid Communications.

The present invention includes the following features:

a) Apparatus and methods of ultrafast, ultrashort, ultrawideband pulsetransmission.

b) Apparatus and methods of transmitting sequences of such ultrafast,ultrashort, ultrawideband pulses.

c) Apparatus and methods of pulse interval modulating such sequencesaccording to a macro-coded scheme.

d) Methods of pulse interval modulating such sequences within amicrowindow of the macrowindow set by the code such that information canbe encrypted in that microwindow.

e) Codes stored in matrix form as associative memories and withsuperframes of received signals matched against the stored codes.

f) Codes which are orthogonal codes and the temporal coding of thesequence of ultrafast, ultrashort, ultrawideband pulses constitutes thecarrier for the transmission.

g) A homodyne, not a synchronous heterodyne, receiver.

h) An acquisition system/matched filter/correlators which synchronizesto a superframe transmission and assigns such transmissions to anappropriate decoding modem on the basis of code recognition.

i) Multichannel operation which provides high overall data rate (e.g.,500 mbs for maximum multichannel operation).

The attached paper entitled "Comparison of Communications . . . anddisclosure statement" and the paper entitled "Reference" filed herewithare incorporated herein by reference.

Summarizing, according to the invention, an ultrashort pulse timehopping code-division-multiple-access (CDMA) RF communications system inthe time frequency domain comprises a transmitter including:

a) a short duration pulse generator for generating a short durationpulse in the picosecond to nano-second range and a controller forcontrolling the generator,

b) code means connected to the controller for varying the time positionof each short pulse in frames of pulses in orthogonal superframes ofultrafast time hopping code division multiple access format,

c) precise oscillator-clock for controlling such timing,

d) encoding modems for transforming intelligence into pulse positionmodulation form,

e) antenna/amplifier system connected to said means for generating forreceiving and broadcasting said short duration pulse as a codedbroadcast signal,

receiver means, said receiver means including:

a) antenna/amplifier system for receiving the broadcast signal,

b) homodyne receiver for receiving and decoding the coded broadcastsignal, and

c) one or more utilization devices connected to the homodyne receiver.The coding means generates sequences of ultrafast, ultrashort,ultrawideband pulses, and an interval modulator for interval modulatingthe sequences according to a macrowindow encoded format. The macrowindowencoded format set by the assigned code includes microwindows and thepulse interval modulator modulates the position of an individual pulsewithin a microwindow of each macrowindow set by the code such thatinformation can be encrypted in each of the microwindow. The code meansincludes codes stored in matrix form as associative memories and withsuperframes of received signal representing the full assigned code,orthogonal to other assigned codes, matched against the stored codes.Preferably, the codes are orthogonal codes with the temporal coding ofthe sequence of ultrafast, ultrawideband pulses constituting the carrierfor transmission by the antenna system.

The homodyne receiver includes a bank of decoder/modems, an acquisitionsystem/matched filter for synchronizing to a superframe transmission,identifying coded sequencers in the superframe and assigning thetransmissions to a selected decoder/modem on the basis of coderecognition. The system is adapted for multichannel operation andprovides a high overall data rate in the 500 mbs range for maximummultichannel operation.

While preferred embodiments of the invention have been illustrated anddescribed, it will be appreciated that other embodiments, adaptationsand modifications of the invention will be readily apparent to thoseskilled in the art and embraced by the claims appended hereto.

What is claimed is:
 1. An ultrashort pulse time hoppingcode-division-multiple-access (CDMA) RF communications system in thetime frequency domain, comprising:transmitter means, said transmittermeans including:a) means for generating a short duration pulse in thepicosecond to nano-second range and means for controlling said means forgenerating, b) coding means connected to said means for controlling forvarying the time position of each said short duration pulse in frames ofpulses in orthogonal superframes of ultrafast time hopping code divisionmultiple access format, c) precise oscillator-clock means forcontrolling such timing, d) encoding modems for transforminginformation, voice and data signals into pulse position modulation form,e) antenna means connected to said means for generating for receivingand broadcasting said short duration pulse as a coded broadcast signal,receiver means, said receiver means including:a) antenna means forreceiving said coded broadcast signal, and b) homodyne receiver meansfor receiving and decoding said coded broadcast signal.
 2. Thecommunication system defined in claim 1 wherein said coding meansincludes means for generating sequences of ultrafast, ultrashort,ultrawideband pulses, means for interval modulating said sequencesaccording to an orthogonal code which positions each pulse within a setmacrowindow.
 3. The communication system defined in claim 2 wherein saidmacrowindow set by the assigned code includes microwindows and saidmeans for pulse interval modulating, modulates the position of anindividual pulse within a microwindow of each macrowindow set by theassigned code such that information is encrypted in each saidmicrowindow.
 4. The communication system defined in claim 1 wherein saidcoding means includes codes stored in matrix form memories and withsuperframes of received signals representing the assigned code,orthogonal to other assigned codes, matched against said stored codes.5. The communication system defined in claim 4 wherein said codes areorthogonal codes with the temporal coding of the sequence of ultrafast,ultrashort ultrawideband pulses constituting the carrier fortransmission by said transmit antenna means.
 6. The communication systemdefined in claim 4 wherein said homodyne receiver means includes a bankof decoder/modems, an acquisition system/matched filter forsynchronizing said orthogonal superframe for transmission, identifyingcoded sequencies in the superframe by said acquisition/matched filterand assigning said superframe transmissions to a selected decoder/modem.7. The communication system defined in claim 1 which is adapted formultichannel operation and which provides a high overall data rate formaximum multichannel operation.
 8. The RF communication system definedin claim 1, comprising means for increasing the number of orthogonalcodes available wherein the number (N) of orthogonal codes availablecomprising a first family of codes, the number (Y) of orthogonal codesavailable to a second family of codes, and the number (N) of orthogonalcodes available to an n'th family, means entraining said families, andusing matched filter acquisition such that the total number of codesavailable is x X y X . . . X N, wherein X is the number of codes in thefirst family; Y is the number of codes in the second family, and N isthe number of codes in the n'th family.
 9. The RF communication systemdefined in claim 1, comprising means for increasing the number oforthogonal codes available wherein the clock rate for a first set of "a"orthogonal codes is A cycles/sec, the clock rate for a second set of "b"orthogonal codes is B, and the clock rate for an n'th set of "n"orthogonal codes is N, then by clock syncopation, and means includingseparate matched filters at clock rates A, B, . . . N, the total numberof codes available is a+b+ . . . +n, where "a" is the number of codes inthe first set; "b" is the number of codes in the second set; . . . and"n" is the number of codes in the `n'th` set; A is the first clock rate;. . . N is the "n"th clock rate, if the matched filter outputs are notentrained, and a X b X . . . X n if the matched filter outputs areentrained.
 10. A transmitter for ultrashort pulse time hoppingcode-division-multiple-access (CDMA) RF communications system in thetime frequency domain, comprising:a) a short duration pulse generatormeans for generating a short duration pulse in the picosecond tonano-second range and means for controlling said short duration pulsegenerator, b) a coding unit connected to said means for controlling forvarying the time position of each said short duration pulse in frames ofpulses in orthogonal superframes of ultrafast time hopping code divisionmultiple access format, c) a precise oscillator-clock for controllingsuch timing, d) encoding modems for transforming information, voice anddata signals into pulse position modulation form, and e) an antennaconnected to said short duration pulse generator for receiving andbroadcasting said short duration pulse as a coded broadcast signal.